In recent years, image capturing using terahertz waves has been anticipated in fields such as security inspection, biotechnology, and the like. In these fields, polarized imaging for splitting terahertz waves into ordinary light (rays) and extraordinary light (rays) to perform image capturing is considered to be especially useful.
Meanwhile, terahertz waves are invisible light, and thus positions of the light cannot be accurately determined. When an attempt is made to discriminate the positions of the light, a method of inputting guide light to be minitored on the same axis as the invisible light is considered. However, since wavelengths of the light differ, behaviors inside an optical structure differ, and accurate monitoring is impossible.
As a method of monitoring a position of light, a method of using an optical structure as described in Non-Patent Literature 1 is considered. In Non-Patent Literature 1, a Wollaston prism is coupled to another Wollaston prism at a rear stage thereof. In the same literature, there is a proposal for an optical structure in which different wavelengths of light are output at the same split angle in spite of being polarized and split.
[Non-Patent Literature 1] Gerald Wong, Roger Pilkington, and Andrew R. Harvey, “Achromatization of Wollaston polarizing beam splitters,” Optics Letters 36, 8 1332-1334 (2011)